This will create a listbox with 5 items. As multiple attribute value is specified as ="multiple" so it gives ability to select more than one item from the box by holding ctrl key or by dragging through items from the mouse.

Doctype defines as "document type declaration" (DTD). All HTML pages should contain a declaration to define which HTML version we are using in our page. it gives important instruction to web browser about page's HTML version type. It also allows web validator to check the syntax of page.